fix: preserve binary string planner semantics

[ck89119]

What type of PR is this?

• API-change
• BUG
• Improvement
• Documentation
• Feature
• Test and CI
• Code Refactoring

Which issue(s) this PR fixes:

issue #25295

What this PR does / why we need it:

This is layer 2 of the replacement for draft PR #26750 and depends on layer 1.
Because the dependency branch lives in a fork, this draft is temporarily cumulative against main; after layer 1 merges, only the planner/scalar commit remains.

It closes planner and scalar-function binary-string semantics:

• selects byte or character algorithms from the subject argument and selected row;
• propagates per-row provenance through scalar, conditional, regexp, cast, and string functions;
• keeps explicit CAST/CONVERT ... AS CHAR as text semantics;
• infers materialized binary types for CTAS and set operations from expression results;
• fixes empty binary literal formatting and CHAR(... USING charset) parsing.

Validation:

• full parser, planner, and function package tests passed;
• owning-package build and vet passed;
• focused mixed-row binary/text/NULL/select-list regression passed;
• CI-equivalent incremental coverage for this layer: 76.27% (707/927).